1. Field of the Invention
The invention relates to a process for the galvanic deposition of nickel from nickel sulfamate and nickel chloride containing electrolytes using nickel anodes in bags.
2. Description of the Prior Art
The galvanic deposition of thick nickel layers is used to an increasing extent because, using this method, nickel plated objects having complex shapes can be produced economically, even in small numbers. Preferably, an electrolyte is used for this process consisting of nickel sulfamate to which nickel chloride has been added in order to improve the anode solubility.
Furthermore, processes are known in which nickel plates or nickel pellets, inserted into titanium or plastic baskets, are used as anodes. These are suspended in narrow-meshed bags in the electrolyte bath, in order to collect the anode sludge.
In manufacturing hollow parts or other component parts, which are galvanically formed with nickel deposits, and which consist of several individual parts, the joined individual parts could hitherto only be bonded and sealed at the joints by means of partial galvanoplastic processes. This was necessary, because the galvanically deposited nickel was regarded as not being weldable because that region of the component part, which was heated to above 400.degree. C. during the welding, became totally brittle. The cause for this presumably lies within the sulfur portion which is deposited at the same time in the galvanic nickel and that is partially dissolved as nickel sulfide. With increasing temperature, this material collects, to an increasing degree, at the grain boundaries and leads to the formation of a nickel-nickel sulfide eutectic at that point. On heating, the resulting phase diffuses from this point at a rather high rate, into the depth of the nickel material. In fact, the diffusion of the nickel-nickel sulfide eutectic occurs only when the melting point of the eutectic is reached. This melting point is about 645.degree. C. However, the diffusion process, at a lesser rate, can be detected from 400.degree. C. onwards. A marked brittleness of the material can be detected at those sites of the nickel structure, that were reached by the diffusing nickel sulfide phase, and that were subsequently mechanically stressed.
These facts have been documented, but there is no data in the literature concerning the temperature strength relationships, and especially concerning the 0.2% yield strength of galvanic nickel deposits at temperatures above 650.degree. C. or that the values for the tensile strength decrease rapidly at temperatures above 400.degree. C.
In spite of the fact that this disadvantage of galvanically deposited nickel has been known for a longe time, no efforts have hitherto been made to indicate the factors that influence the brittleness that occurs at elevated temperatures and to show how these may be eliminated.